The location of a mobile wireless device utilizes one or more positioning techniques in order to estimate the location and in some cases, the speed, direction-of-travel, and altitude of the mobile device (also known as the mobile, mobile station (MS), handset, or user equipment (UE).
Determining the position of a mobile device involves two main steps: collection of radio signal measurements, and a local or remote position estimate computation based on those measurements. Signal collection can be performed by a receiver within or co-located with the mobile device.
Hybrid positioning, using multiple methods positioning methods, is used to increase the accuracy or yield of a location estimate.
Location Technique Standardization
The location techniques used in different wireless communications networks (WCN) using different radio transmission technologies are subject to standardization. Notable standards development organizations include the 3rd Generation Partnership Program (3GPP), the 3rd Generation Partnership Program 2(3GPP2), and the Open Mobile Alliance (OMA.)
Location techniques standardized for the Global System for Mobility (GSM) are detailed in 3GPP Technical Specification TS 43.059, “Functional stage 2 description of Location Services (LCS) in GERAN”. The GSM location techniques include: cell coverage based positioning, Enhanced Observed Time Difference (E-OTD) positioning, Assisted Global Navigation Satellite System (A-GNSS) based positioning; and Uplink Time Difference of Arrival (U-TDOA) positioning.
Location techniques standardized for the Wide-band CDMA system (better known as Universal Mobile Telecommunications System (UMTS)) are detailed in 3GPP Technical Specification 25.305, “Stage 2 functional specification of User Equipment (UE) positioning in UTRAN.” The UMTS location techniques include: cell coverage based positioning, Observed Time Difference Of Arrival (OTDOA) positioning, A-GNSS based positioning, and U-TDOA.
Location techniques standardized for the Evolved Universal Mobile Telecommunications System (more commonly known as the Long-Term Evolution or LTE system) are described in 3GPP Technical Specification 36.305, “Stage 2 functional specification of User Equipment (UE) positioning in E-UTRAN.” The current (release 9) LTE location techniques include: uplink and downlink cell coverage based positioning, Observed Time Difference Of Arrival (OTDOA) positioning, and A-GNSS based positioning. While not yet standardized, the U-TDOA positioning technique is applicable to LTE.
Location techniques standardized for the IS-95 (CDMAOne) and IS-2000 (CDMA-2000) radio access networks are described in 3GPP2 Specifications C.S0022-0, “Position Determination Service Standards for Dual Mode Spread Spectrum Systems,” and C.S0022-A “Position Determination Service for CDMA2000 Spread Spectrum Systems.” The 3GPP2 standardized techniques include cell-based positioning, Advanced Forward Link Trilateration (AFLT) and Assisted Global Positioning Satellite positioning.
Mobile-Based and Mobile-Assisted Location Techniques
Mobile location techniques use radio signals collected at the mobile device to generate a location estimate. Mobile Location techniques for wireless communication devices can be broadly categorized as mobile-based or mobile-assisted dependent on the use of precursor information and where the final location estimate is calculated. Mobile location techniques can be combined with each other and with network-based location techniques (Uplink time-difference-of-arrival (U-TDOA) and/or angle of arrival (AoA)) to achieve the highest yields and accuracies.
The least accurate, but highest availability mobile location method is called cell-ID Positioning. The cell-ID, cell coverage based positioning or cell-ID positioning technique uses radio broadcast information from the cellular network already in use to allow mobility. Translation of the cell-ID (or cell/sector ID) into a latitude and longitude may be performed at the mobile or at a networked, landside server. The basic cell-ID location can be improved with the addition of time or power-based ranging.
Enhanced Cell-ID (ECID) positioning uses cell-ID positioning with the addition of timing and power measurements made by the mobile of the downlink broadcast beacon from the serving and neighboring cell sites. ECID is considered a mobile-based location technique as the signal collection and measurement is performed at the mobile but location calculation is generally preformed at a network server. Although not explicitly standardized this technique has been commercially deployed.
Enhanced Observed Time Difference (E-OTD) positioning is a mobile-based technique for unsynchronized wireless networks. The EOTD system uses the time-of-arrival of a cell broadcast radio signals at the mobile device receiver. Collected signal timing and cell-ID information is then transmitted to a networked, landside server. The EOTD system must supply the geographic location and the collected timing offsets for each cell transmitter in order to determine a location estimate.
A variation of ECID is Radio Fingerprinting. Radio Fingerprinting may be implemented as a mobile-based technique uses downlink (network-to-mobile) radio signal collected by the mobile. Radio Fingerprinting is also called Wireless Signatures, Multipath Fingerprinting, Database Correlation Method (DCM), or Pilot Correlation. The radio fingerprinting technique uses the propagation characteristics of a reflected and refracted radio signal as received by the mobile device to determine a location by matching with a signal from a database of recorded or modeled signal propagation characteristics (also called radio fingerprints). Although not explicitly standardized this technique has been commercially deployed.
Observed Time Difference Of Arrival (OTDOA) is a mobile-based technique that uses the relative timing offset of the broadcast beacons from different cells. A time difference of arrival technique, OTDOA requires a minimum of three cell beacons to determine a location. The purely downlink-TDOA based location estimation will typically be combined with a cell-ID-with-ranging location estimate and databased information on the geographic location of the reported cell beacon transmitter antenna to create a final hybrid location estimate.
Advanced (or Enhanced) Forward Link Trilateration (AFLT or EFLT) is a mobile-based technology used only in WCN with precise timing and base station synchronization. Mobile-based AFLT requires reception of beacons from four or more cells and knowledge (normally via cell broadcast) of the geographic locations of those cells. Network-assisted AFLT requires reception of three or more cell beacons by the mobile device and a communications channel to a landside server which uses the mobile device-collected signal measurements and geographic locations of the cells to calculate a location estimate.
Assisted Global Navigation Satellite System (A-GNSS) and Assisted Global Positioning Satellite positioning is technically a mobile-based technique since the satellite broadcast signals used for location are collected at the mobile device via a specialized receiver and antenna. Network-generated assistance information is transmitted to the receiver to increase receiver sensitivity and decrease the time-to-first-fix. A-GNSS may be deployed as network-assisted, mobile-based where the signals are collected and final location is produced local to the mobile device, or as network-assisted, network-computed, where the collected signal information is transmitted to a landside server for final location estimation.
The inventive techniques and concepts described herein apply to time and frequency division multiplexed (TDMA/FDMA) radio communications systems including the widely used IS-136 (TDMA), GSM, and OFDM-based wireless systems, such as the IEEE 802.16e “WIMAN” and 802.20 “WIMAX” system and the 3GPP Long Term Evolution (LTE and LTE Advanced) system, as well as code-division radio communications systems such as CDMA (IS-95, IS-2000) and Universal Mobile Telecommunications System (UTMS), the latter of which is also known as W-CDMA. The Global System for Mobile Communications (GSM) model used herein as examples is an exemplary but not exclusive environment in which the present invention may be used.